Hammond-Accutronics reverb tank that does not have the standard code

[pullshocks]

Going through my parts box I found an old reverb tank I bought off craigslist and never used.  It is 16.5" length, 2 springs.  I am hoping it is a 4AB3C1B type, but it does not have a code of that type.

There is a sticker inside that says "Reverberation Unit Acutronics Janesville Wisconsin Subsidiary of Hammond Corporation" , that gives the patent numbers. 

On the outside surface it has the numbers 820209 ink stamped, and 1122 punched in the surface.  Also, it has the letter C ink stamped on the inside.

If it is the right type I would like to use it for a Fender or 1 tube reverb in my next build

Can anybody help with this?  I would like to verify it is the right type before purchase a reverb transformer

Thanks

[2deaf]

What is the DC resistance of the input and of the output?

[eleventeen]

Right type or wrong type, you're still gonna have to buy a reverb transformer, right?

[pullshocks]

2deaf, I get 183 ohms on the input jack, and 181 on the output jack

Eleventeen, you are right, what I meant to say is if I have to buy both transformer and tank I will probably just go with an effects loop and use the Alesis Nanoverb.

[2deaf]

You have the equivalent of a 4FBxxxx tank.

[kagliostro]

The more expert will say if it worth to give a try to a cap coupled Reverb circuit

ECC83 - ECL82(6bm8)


6BM8(ECL82)


12DW7


EL84 only driver


ECC82 - http://www.valvewizard.co.uk/reverbdriver.html


ECC82 - http://www.valvewizard.co.uk/reverbdriver.html


Here you can find some doumentation you can use as to identify your tank
https://www.amplifiedparts.com/tech-corner/spring-reverb-tanks-explained-and-compared

Franco

[pullshocks]

Thanks 2Deaf and Franco.

I found some web sites with Ampeg repair information that mention a "C" reverb tank being used in many ampeg amps.  This is stamped in ink with the letter C

One other interesting thing is that it has the spring lock lever. 

[2deaf]

I have a Gibbs tank with the 1122 stamped into the housing and the letter "C" stamped on the inside near the input and it is a type F tank.  That letter "C" doesn't have anything to do with the modern type C tanks.

[pullshocks]

Yes the "C" ink stamp on the inside of mine is also near the input. 

So the first 3 digits are 4FB.  I don't know how to determine the decay time, so 4th digit is a ?.  Both phono jacks are grounded, so 5th digit is 1.  It has the locking lever but I don't know the code for that.  So the 6th digit is "not 1".  The mounting plane is unknown, so the 7th digit is a question mark.

So this is a 4FB?A?? tank.   

Next question is whether it actually works. 

[kagliostro]

Next question is whether it actually works.

As you were able to measure the resistence of input and output we can suppose it will work

but only a try can say for sure

Franco

[VMS]

ECC83 - ECL82(6bm8)

This circuit looks interesting. What amp is this from and do you have full schematic?


Thanks in advance.

[kagliostro]

It is an old italian guitar amp an FBT 1200 R

here is the schematic





Giulio, my friend, converted it to EL36 tubes because of the high price of the EL503 tubes

http://www.chambonino.com/modify/giumod1.html

Franco

[pullshocks]

How does the reverb sound on that amp?

[kagliostro]

Sorry, never heard, and Giulio was repairing the amp for a customer 


Franco

[Dingleberry]

Hi!

Just accidentally stumbled across this topic and realised that I have two reverb tanks collecting dust in my shelf that fits the pullshocks's description of his craigslist buy.
Both of them are pulls from old Italian amps.
One is from Steelphon Pioneer head and other from unknown model FBT 2x12" combo. Both amps had cap coupled reverb, Steelphon driven by ECL86 and FBT driven by ECL82.
I measured the DCR:s of those tanks input and output transducer and got readings that pretty much verifies that they are 4FBxxxx type tanks.

[pullshocks]

Dingleberry, thanks for adding your info to what the others provided.  This is a great forum.

I have 12DW7, 12AT7 and 6BM8 tubes on hand so I will probably resurrect plans to build a breadboard and experiment with this.

[2deaf]

How are you doing with the breadboarding?

I have a couple of transformerless designs for a 4F tank that you might like to try.  They both stay within the maximum dissipation for their tube type, or at least pretty close.

The 12DW7 driver in response #5 is very bogus and I wouldn't waste any time trying it.   

[pullshocks]

Thanks.  This is really cool.

Breadboard is out there a ways, need to do some fabrication, go through my stock of caps and resistors  and get an order in to Doug for what I don't have on hand.

I will be repurposing a big old chassis I got out of the dumpster at the physics department a long time ago that had about 15 octal sockets, and a few 7 pin sockets...no idea what it was originally.

Will the circuits work ok with lower B+?

[2deaf]

You can run these circuits at a lower voltage, but the headroom will decrease so that you cannot drive the tank as hard.

[Dingleberry]

Nice to see this topic goes strong. Thanks for the schematics 2deaf!
I've been a big fan of Swart reverb, which indeed is implemented with just one 12DW7, but never had an opportunity to peek inside one to check the resistor & cap values and measure the voltages.
I know that Swart amps uses 8FB3C1B tank, but I think that this tank and that 12DW7 driver will lead me into same ballpark.
I have one prototype chassis on hand that has power transformer which gives B+ approximately 350V! Can't wait to get into it!

[pullshocks]

OK I am getting a Princeton Reverb circuit set up on the bread board to  try 2deaf's 12DW7 transformerless reverb circuit.

In the PR, the signal tap off to the reverb driver and the return from the reverb recovery are separated by a 3.3 meg resistor with a parallel 10p capacitor. 

Do I do the same thing for this reverb circuit?

Is there a name for that circuit element, e.g. "reverb splitter resistor?"

Thanks

[2deaf]

In the PR, the signal tap off to the reverb driver and the return from the reverb recovery are separated by a 3.3 meg resistor with a parallel 10p capacitor.
Do I do the same thing for this reverb circuit?

Yes.  You can set up the recovery stage just like the PR instead of the way I have it set up.

[pullshocks]

I plan to use the circuit as you drew it. I just want to verify how to connect it to the signal path, see attached drawing.

I will also need to get some advice about which node to use for the B+ for the driver stage.  I am not using an actual  Princeton Reverb power transformer and need to verify the power supply voltages.

[2deaf]

You really don't want to use the recovery stage the way that I drew it because it isn't intended to be used in a voltage divider like that.

The recovery stage acts like a resistor in parallel with the 500K pot.  When the pot. is turned off, the voltage divider is 3.3M to 500K.  When the 500K pot. is turned clear up, the voltage divider is 3.3M to something way less than 500K at higher frequencies.  At lower frequencies, the 0.0022uf cap. has a lot of impedance and the divider is closer to 3.3M to 500K.  So the dry signal will have a magnitude that is dependent on the 500K pot. setting and the frequency.  There could be a magnitude change in the order of three times between the extremes.

The Fender PR divider is 3.3M to 470K with the 100K reverb pot clear off.  At very low frequencies with the pot. dimed, it is 3.3M to 570K.  At other frequencies and pot. settings, the ratio is between those two extremes.  No matter what you do, the dry signal magnitude will not change much. 

[pullshocks]

I have to confess, that is over my head.  So....should I use the driver as shown, but with the Princeton Reverb recovery circuit??

[pullshocks]

OK I reread post 21 and see that you already said to use the Princeton Reverb recovery.

[pullshocks]

So, I rearranged the "Hoffman Princeton Reverb - No Tremolo" with 2Deaf's 12DW7 transformerless reverb driver from post 15.  Conveniently this is a 3 preamp tube setup which will work out for an existing chassis that I have (Judybox).  I also added a mid control, as well as cathode bias on the power amp, and the  PPIMV as seen in several of Tubenit's designs and elsewhere.

To get the 350 volts on the reverb driver, I propose to connect to node C in the power supply.  In the normal Princeton circuit nothing is connected to node C.  The Duncan PSUD leads me to try 6.8K for the 2nd dropping resistor, to keep the node C voltage at 350, instead of the stock 18K, which gives 320 volts at node C.   

It is my first time using the PSUD, and to be honest I'm a little uncertain if I have the simulation set up correctly. Hopefully it is in the ballpark